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Vitamin A deficiency is very prevalent and contributes substantially to morbidity and mortality among young children in developing countries. We identify and quantify three causes of vitamin A deficiency in young children based on data available in the literature: maternal vitamin A deficiency resulting in low concentrations of vitamin A in breast milk, inadequate dietary intake of vitamin A during and after weaning and prevalent illness. We developed a set of recursive equations to estimate the amount of vitamin A in the liver as a function of age over the first 2 y of life. To apply the equations, we selected a best estimate value for each input parameter as the most representative of a typical child in a developing country. Because of the great variability that exists for each variable, we also carried out sensitivity analyses, substituting more extreme values for input parameters. We then estimated stores, assuming a child in a …